Swap the operands of a select node if the false (the second) operand is 0.

For example, this pattern 
(select (setcc lhs, rhs, cc), true, 0)
is transformed to this one:
(select (setcc lhs, rhs, inverse(cc)), 0, true)

This enables MipsDAGToDAGISel::ReplaceUsesWithZeroReg (added in r152280) to
replace 0 with $zero.

llvm-svn: 152285